This file was created by scanning the printed publication. To enable searches, the text was digitized using OCR software but some spelling errors may occur. CHAPTER 4 Life Histories of Potamodromous Fishes Russell F. Thurow Definitions of potamodromy, potamodromous migrations and movements Potamodromous fishes move and complete their life cycle entirely within freshwater. Myers (1949) proposed the term potamodromous to distinguish freshwater migratory fishes from diadromous fishes, which migrate between the sea and freshwater and oceanodromous fishes that migrate wholly within the sea. Diadromous fishes include anadromous, catadromous and amphidromous fishes (see Chapter 2, Morais and Daverat 2016). Despite its historical precedence, potamodromous has not been broadly accepted. Three other terms, 'non-anadromous', 'resident', and 'inland' are more commonly substituted in the fisheries literature. Unfortunately, these three terms have multiple definitions, as well as regional connotations which may confound their application to a broad geographic area (Gresswell et al. 1997). Consequently, potamodromous provides a more precise and more broadly applicable definition of fishes that remain wholly within freshwater. Although potamodromous fishes are widespread among freshwater fish assemblages, the significance of potamodromy has received far less attention than diadromy (Northcote 1998). Unlike diadromy, no global analysis ofpotamodromous species has been undertaken, and it is limited by the difficulties in amassing information for inconspicuous and little-studied species, especially in the tropics (Flecker et al. 201 0). Potamodromous fishes were included in a group-by-group review by Lucas and Baras (200 1) of the migration and life cycle characteristics of species representative of families of fishes exhibiting migration in fresh and brackish water environments. Lucas and Baras (2001) explained that infon:llation was limited for some groups of freshwater fishes mostly found in tropical freshwater regions. This was partly because USDA-Forest ervice-Rocky Mountain Research Station, 322 East Front Street-Suite 401, Boise, Idaho 83702, USA. 30 An Introduction to Fish Migration of a paucity of infom1ation concerning spatial ecology at the species level; some of these group (Cichlidae haraciformes and Silurifonnes) are very speciose, totaling over 5,000 species and representing nearly 50% of all fish pecies in freshwater (Lucas and Ban1s 2001 . Flecker et al. (20 I 0) reported that in both the tropic and temperate zone, potamodromy is likely the most common fonn ofmigration in stream fi shes. im i larly, Lucas and Baras (200 I) observed that in many large tropical rivers, more than 95% of the migratory fishes are potamodromous. Migration and movements between biomes on a daily seasonal or annual basis, represent a fundamental aspect of the ecology of populations and individuals (Hobson 1999. Despite residing only in freshwater for a variety of reasons, potamodromous fishes move and migrate various distance U1roughout their life c cle. As Dingle and Drake (2007) ob erved our understanding of the movements of organisms has been hindered by impreci e and ambiguous te.m1inology. A a result it may be useful to begin by defining the terms movement and migration. Movement may be defined as the act of changi11g locations or positions. In potamodromous fishes, these movements are most commonly associated with seeking essential resources (i.e., food) and they may be in response to other organisms (i.e. seeking cover from predators). For example, a potamodromous sculpin Cottus spp. residing in a pool may suddenly move and change position' to consume an aquatic insect larvae on the tream substrate. This same sculpin may change its location' in the same pool by moving beneath a boulder to escape an avian predator. Dingle (1996) observed that most movements occur within a relatively well defined area or home range. An organism h·avels or moves within its home range to acquire the resources it needs to survive. The size of the home range wi ll tend to vary depending on the habitat and the size and movement abiliti.es of the organism (Dingle 1996). Consequently, the sculpin in our example above will ha e a much smaller home range compared to the average home range size (mean home range of 146 ha) for a 70- 100 em long muskellunge Esox masquinongy (Miller and Menzel 1986). Movements and associated behaviors within a home range have also been tenned station keeping' and perhaps the most prominent example is foraging (Kennedy 1985 · Di11gle 1996). foraging is a repetitive and meandering movement that focuses on locating resources (food cover or mates). Foraging characteristically occurs on hort timescales and small spatial scales wHhin the home range (Dingle and Drake 2007). ln our examples above depending in part on food availability the much larger and faster swimming muskellunge will potentially forage within a much larger area compared to the sculpin. A specialized form of foraging that includes to-and-fro movements, is the diel vertical movement of fishes such as alewife Alosa pseudoharengus to con ume zooplankton (Jans en and Brandt L980). Another example of a station keeping behavior is the territorial behavior that results in agonistic encounters between individuals. McNicol et al. ( 1985) repotted frequent agonistic interactions between young-of-the-year brook trout Salvelinusfontinalis in a second-order woodland stream. Migration differs substantially from the oft§n repetitive movements within home ranges described above. Home range movements are primarily in response to local resources. Migration is considered a more specialized type of movement often, Life Histories ofPotamodromous Fishes 31 but not necessarily occurring at larger temporal and spatial scales. Dingle (1996) emphasized that migration differs from other types of movements both qualitatively and quantitatively. Unlike the sculpin, muskellunge, and alewife movements described above, Dingle ( 1996) observed that migration is not a proximate response to resources nor does it serve to keep an organism in its habitat. Rather, migration results in fishes moving from one habitat and relocating to another habitat outside their home range. Dingle ( 1996) observed that the most distinctive feature of migration is that migrants do not respond to sensory cues from resources (e.g., food or shelter) that would typically elicit responses. For example, during their annual migration to spawning sites, adult walleye Stizostedion vitreum vitreum may feed or temporarily seek shelter. However, unlike the above referenced foraging movement of a muskellunge within its home range, the presence of an abundant food source or suitable cover will not cause migrating walleye to stop. Their upstream migration ceases only when adult walleye arrive at their spawning location (i.e., Crowe 1962). Migration involves two levels, the behavioral level that applies to individuals and the ecological level that applies to populations (Dingle and Drake 2007). Therefore, a broad conceptual understanding of migration encompasses both its mechanism and its function. Northcote (1978) distinguished migration from other types of fish movements and suggested four main features : (1) resulting in an alternation between two or more well-separated habitats; (2) occurring with regular periodicity (often seasonal) within the individual lifespan; (3) involving a large fraction of the population; and (4) being directed rather than a random wandering or passive drift. Decades later, Dingle and Drake (2007) suggested that migration represents four different but overlapping concepts which are very similar to those ofNorthcote (1978). The concepts of Dingle and Drake (2007) are also applicable to potamodromous fishes: (1) a type of locomotory activity that is notably persistent, undistracted, and straightened out (i.e., fall downstream migrations of adult westslope cutthroat trout Salmo clarkia lewisii to overwintering areas in large pools) (Bjornn and Mallet 1964); (2) a relocation of the animal that is on a much greater scale, and involves movement of much longer duration, than those arising in its normal daily activities (i.e., spring upstream migrations of mature walleye to spawning areas) (Crowe 1962); (3) a seasonal to-and-fro movement of populations between regions where conditions are alternately favorable or unfavorable (i.e., summer upstream migrations of brook trout seeking cold water refugia (Petty et al. 2012) followed by fall downstream migrations to more suitable overwintering habitats) (Chisholm et al. 1987); and ( 4) movements leading to redistribution or dispersal within a spatially extended population (i.e., downstream drift of newly hatched white sucker Catostomus commersoni larvae to areas with higher zooplankton production) (Corbett and Powles 1986). Dingle and Drake (2007) explained that migration of types 1 and 2 relate to individual organisms, while types 3 and 4 explicitly concern populations. Further, type 1 migration describes a process, whereas the other three migrations describe the outcomes (for individuals or populations) of migration by individuals. Baker (1978) proposed that the sum of all migrations and movements during ~n organism's lifetime be termed a 'lifetime track'. An organism's lifetime track ls essentially the time series of its successive locations throughout its lifetime 32 An Introduction to Fish Migration (Dingle and Drake 2007). Technological advances in tracking devices now allow